1. Field of the Invention
The present invention relates to a composite fiber having a low content of electrically conductive carbon black and having good destaticizing performance over a long period of time. This composite fiber suppresses dusting, maintains excellent conducting performance over a long period of time, and can be mixed or woven with other fibers to give garments having good ironing resistance and good color fastness. When used as a charging brush for copying machines and printers the composite fiber allows for the production of high-quality printed images over a long period of time.
2. Discussion of the Background
A variety of electrically-conductive fibers with good destaticizing properties have been proposed. For example, electrical conductivity is introduced by metallic plating on the surface of a non-conducting fiber or by formation of an electrically-conductive coating layer on a fiber from resin or rubber in which electrically-conductive carbon black is incorporated. Drawbacks are their complex and difficult production processes or their easy loss of electrical conductivity during scouring, involving chemical treatment, and in actual use, involving wearing and repeated washing.
Another example of an electrically-conductive fiber is a metallic fiber, such as steel fiber. Although such metallic fiber is known for its good destaticizing properties, it is expensive and incompatible with ordinary organic matters. This causes troubles in weaving and dying steps. Moreover, it easily breaks and drops during washing. Its electrical conductivity gives an unpleasant feel and causes sparking and cloth melting.
A further example of an electrically-conductive fiber is produced from a polymer containing uniformly dispersed electrically-conductive carbon black. A disadvantage of this type of fiber is its difficult production process due to a large content of electrically-conductive carbon black. The yields are poor and the production costs are high. Its fiber properties are poor and it can only be produced with difficulties by a special process.
New ideas have been proposed in order to address the above problems. For example, U.S. Pat. No. 3,803,453 discloses a composite fiber of sheath-core type in which the core polymer contains an electrically-conductive carbon black and the sheath is made of an ordinary fiber-forming polymer. It is limited in its core size (smaller than 50%) so that it exhibits necessary fiber properties. This leads to a thick sheath, which is non-conductive, and a core highly filled with carbon black.
Japanese Patent Publication No. 44579/1978 attempts to solve the problem of the above U.S. patent. It discloses an electrically-conductive composite fiber in which the core contains electrically-conductive carbon black and is only partly covered by a sheath. However, it has poor chemical resistance and durability and core-sheath separation occurs because the core is not completely covered by the sheath.
Further, Japanese Patent Laid-open No. 152513/1977 discloses a composite fiber of side-by-side configuration which is composed of a layer of electrically-conductive polymer containing an electrically-conductive carbon black and a layer of non-conductive polymer containing no carbon black. The two polymers are of the same type. This electrically-conductive fiber has also poor chemical resistance and durability because the layer containing the electrically-conductive carbon black is exposed at the surface.
On the other hand, Japanese Patent Laid-open Nos. 147865/1978 and 34470/1979 disclose an electrically conductive fiber which is composed of a fiber-forming polymer and a linear polymer containing a streakily dispersed organic electrically-conductive substance. This fiber is less sensitive to peeling and surface wearing and has improved washing durability because its electrically-conductive component is enclosed in the fiber.
The disadvantage of this fiber is low strength because the linear polymer containing the organic electrically-conductive substance is dispersed and mixed discontinuously in the longitudinal direction of the fiber-forming polymer. The linear electrically-conductive polymer has no contribution to fiber strength and is completely incompatible with the linear polymer. In addition, the electrical conductivity of this fiber fluctuates depending on the dispersion of the electrically-conductive polymer. Therefore, it is difficult to control manufacturing conditions and product quality. In the case where a polymer is mixed with and dispersed in an incompatible polymer, the dispersed component is not completely enclosed in the matrix component, but is partly exposed at the surface. Therefore, the dispersed component, namely the electrically-conductive polymer, will partly drop off. In addition, the productivity of the production process of this fiber is poor because it suffers excessively large ballooning which stains spinnerets and causes fiber breakage.
Other electrically-conductive composite fibers are disclosed in Japanese Patent Laid-open Nos. 134117/1979, 132624/1986, and 279416/1997. They are constructed such that the electrically-conductive polymer layer partly is exposed at the fiber surface. They wear only a little by friction with metal in fiber production and fiber processing. The constituent components do not separate from each other and the electrically-conductive component does not drop off.
The conventional electrically-conductive composite fiber composed of an electrically-conductive polymer layer and a non-electrically-conductive polymer layer poses no problems during production. However, one disadvantage of this fiber is the decrease in conductivity due to peeling after prolonged use. The electrically-conductive composite fiber is usually mixed with an ordinary fiber when it is used for garments, such as uniforms. Such mixed fabrics are not satisfactory when dyed because of the poor color fastness of the electrically-conductive fiber.
In the conventional technology of electrically-conductive fiber for garment use, no attention has been paid to the long-term durability of conductivity, peel resistance of constituent components, and performance in use.
In addition, there has not been any electrically-conductive composite fiber for non-garment applications which exhibits stable conductivity that is not affected by temperature or environment, has a low starting voltage, good destaticizing performance at a high applied voltage, very little decrease in destaticizing performance after prolonged use, and ability to produce sharp images continuously over a long period of time when used in printers.
It is an object of the present invention to provide an electrically-conductive composite fiber which is not sensitive to wear or component separation during its production or its processing into fabrics, but keeps its good initial performance even after prolonged use in a fabric.
It is another object of the present invention to provide an electrically-conductive composite fiber which when mixed with another fiber and subsequently dyed exhibits such good color fastness that no color migration to the other fiber occurs.
These and other objects are achieved according to the invention, the first embodiment of which includes an electrically-conductive composite fiber, comprising:
(A) an electrically-conductive polymer layer; and
(B) a protective polymer layer.
Another embodiment of the invention includes a charging brush or a destaticizing brush for a printer or a copying machine, comprising:
(A) an electrically-conductive polymer layer; and
(B) a protective polymer layer.